The Quality of Service (QoS) concept of Aggregated Maximum Bit Rate (AMBR) was introduced for Evolved-Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access Network (E-UTRAN) in a Third Generation Partnership Project (3GPP) release and has then been adopted for Global System for Mobile communication (GSM) Enhanced Data rates for Global Evolution (EDGE) Radio Access Network (GERAN) and UTRAN in another release of 3GPP. The AMBR is a QoS parameter that is used to police/shape the bit rate of multiple non-Guaranteed Bit Rate (GBR) bearers belonging to the same user equipment.
There are two variants of AMBR: Access Point Name (APN)-AMBR and User Equipment (UE)-AMBR. The APN-AMBR is enforced for all non-GBR bearers belonging to the same user equipment that are associated with the same APN. For example a user equipment may have a default bearer and several non-GBR dedicated bearers for a single Packet Data Network (PDN)-connection activated at the same time. A user equipment may also have multiple PDN-connections active at the same time to the same APN e.g. in case the user equipment is acting as a router. All those bearers are then policed by the same APN-AMBR. According to the concept of APN-AMBR any bearer may use the full bit rate of the APN-AMBR if no traffic is transmitted on any of the other bearers, but if traffic is transmitted on multiple bearers at the same time then the aggregate traffic is policed so that the total maximum bit rate does not exceed the APN-AMBR. In a case of Long Term Evolution, i.e. 4th Generation (4G), access, the APN-AMBR is part of the user equipment's subscription data and is provided by the Home Subscriber Server (HSS) to the Mobility Management Entity/Serving General Packet Radio Service (GPRS) Support Node (MME/SGSN). For the case of 2G/3G access, it is the Home Location Register (HLR) that provides the user equipment's subscription data.
The MME/SGSN provides the subscribed APN-AMBR to the PDN Gateway (PGW)/Gateway GPRS Support Node (GGSN), which in turn provides this value to the Policy and Charging Rule Function (PCRF) in case dynamic Policy and Charging Control (PCC) is deployed. The PCRF may then authorize a different value and send this back to the PGW/GGSN over the Gx interface, in case of GPRS. The PGW/GGSN in turn forwards this value to the MME/SGSN and further on to the user equipment. The enforcement of APN-AMBR in the Down Link (DL) direction is done in the PGW/GGSN. Enforcement of APN-AMBR in the Up Link (UL) direction is done in the user equipment and in the PGW/GGSN. Enforcement is done also in the PGW/GGSN simply for the reason that an operator may not trust that a certain user equipment implements UL APN-AMBR enforcement.
The UE-AMBR, on the other hand, is a QoS parameter that police/shape the bit rate of all non-GBR bearers of a user equipment regardless of the APN. It may be viewed as the user equipments maximum allowed transfer rate according to the subscription to an operator's services. The UE-AMBR is, just as the APN-AMBR, part of the users subscription data and is received by the MME/S4-SGSN from the HSS or HLR. The enforcement of UE-AMBR is done in the Radio Access Network (RAN), i.e. eNodeB for EUTRAN, both for UL and DL. The value that is used by the RAN is actually not the subscribed UE-AMBR. The MME/S4-SGSN uses an algorithm that calculates the sum of all authorized APN-AMBRs for all active PDN-connections going to different APNs up to the value of the subscribed UE-AMBR, i.e.:Used UE-AMBR=MIN(SUM(authorized APN-AMBR),subscribed UE-AMBR)
This is the value that is sent to the RAN for enforcement of UE-AMBR. In case the authorized APN-AMBR of one or several PDN-connections to different APNs changes or in case PDN-connections to new APNs are established or released, the used UE-AMBR is re-calculated by the MME/SGSN and an update is then sent to the RAN
During the design of Evolved Packet System (EPS) it was decided that it should be possible to change the APN-AMBR by the use of PCC, i.e. it should be possible to upgrade/downgrade authorized APN-AMBR from the PCRF. It has been decided in the standard that all PDN-connections going to the same APN must end up in the same PGW and consequently at the same PCRF. Therefore it was possible to control the APN-AMBR through PCC.
However it was deemed impossible to control the UE-AMBR in the same way for the single reason that in case a user equipment establishes multiple PDN-connections to different APNs, e.g. one PDN-connection activated for regular Internet access and at the same has one PDN-connection established to a corporate APN, then those two PDN-connections may end up on different PGWs and on different PCRFs. If UE-AMBR was to be controlled by the use of PCC then different PCRFs may attempt to control the UE-AMBR at the same time and thus sending contradicting information back to the MME/SGSN. This may be illustrated with the example shown in FIG. 1. The MME/SGSN 101 receives the UE-AMBR. The enforcement of the UE-AMBR is done in the RAN 103. However, as there are two PDN connections 105a, 105b, they end up in different PGWs 109a, 109b and on different PCRFs, e.g. PCRF1 113a and PCRF2 113b. PCRF1 113a may have a UE-AMBR with the value e.g. X, and PCRF2 113b may have a UE-AMBR with a value e.g. Y. Thus, the MME/SGSN 101 will receive contradicting information from PCRF1 113a and PCRF2 113b. FIG. 1 is only an example using LTE access, but other access types such as e.g. 2G/3G is also applicable.
As a consequence the UE-AMBR can not be dynamically changed by PCC, but is always upper bounded to the subscribed value received from the HSS. An operator that wants to e.g. temporarily promote or upgrade a user equipment to a higher UE-AMBR would have to do so by changing subscription data in the HSS.